The transformer differential protection relay MRDT4 is specifically tailored to the protection of two winding transformers. The device offers in addition to the differential protection various communication and backup protection functions. Furthermore the MRDT4 can also be used as a cost-optimized generator differential protection device, where it is even possible to have a step-up transformer integrated into the protection zone. The protection functions of the MRDT4 have been adapted to comply with the requirements of the VDE‑AR‑N‑4110:2018.